In order to keep constant a space (cell gap) between two substrates in liquid crystal display panels, spacer particles such as glass beads and plastic beads having a predetermined particle diameter have been conventionally used; in recent years, processes for forming a columnar spacer by photolithography using a radiation-sensitive resin composition have been employed.
Furthermore, radiation-sensitive resin compositions have often been used for forming TFT element planarization films of a transparent insulative film formed between a thin film transistor (TFT) and a transparent electrode of liquid crystal display panels or protective films to prevent damage or degradation of color filters and also to coat steps between pixels of color layers.
Furthermore, radiation-sensitive resin compositions have been used for forming microlenses as imaging optics of on-tip color filters of facsimiles, electronic copiers, solid-state image sensor, etc. or as optical materials of optical fiber connectors.
It is required that the resin films, formed form these radiation-sensitive resin compositions, have the property of solubility in a developer of an alkaline aqueous solution and also, after curing through development, the property of alkali resistance. Therefore, it has been heretofore publicly known that such requirement can be satisfied by including as essential substituents a carboxyl group of an alkaline-soluble group and an epoxy group that reacts with the carboxyl group to lose alkaline solubility and to gain curability itself upon heating.
At first, mixture systems of a polymer soluble in an alkaline aqueous solution (carboxyl group-containing polymer) and a resin having a substituent reactive with the carboxyl group (epoxy group, etc.) have been used as the resin compositions containing the carboxyl and epoxy groups as essential substituents; however, the radiation-sensitive resin compositions containing these resin compositions as a base polymer are unsatisfactory for resolution and taper shape of patterns when developing by alkaline aqueous solution, therefore, the improvement has been demanded. In order to improve these problems, efforts have been made to develop a polymer having carboxyl and epoxy groups in one polymer chain. However, two-component copolymers of carboxylated monomer and epoxidized monomer have been unsuccessful due to gelatinization caused by the reaction between the carboxyl group and epoxy group during polymerization reaction. As a result of further trials, a polymer having both carboxyl and epoxy groups in one molecule has been completed by using a monomer other than the two kinds of monomers as a third monomer in order to suppress the reaction between the carboxyl group and epoxy group, and a radiation-sensitive resin composition is attained by containing the polymer including a third component as a base polymer (see Patent Document 1). The resin composition of this type has been still widely used for spacers of liquid crystal display panels (see Patent Document 2), TFT element planarization films (see Patent Document 3), and protective films for color filter (see Patent Document 4). Patent Document 1: Japanese Unexamined Patent Application No. H06-43643
Patent Document 2: Japanese Unexamined Patent Application No. 2006-308612
Patent Document 3: Japanese Unexamined Patent Application No. 2007-171572
Patent Document 4: Japanese Unexamined Patent Application No. 2006-83248